A flat belt for transmission or transportation is normally used in the endless form which is made by joining both ends of the flat belt. The finger joint is a well-known method for joining both belt ends. In this method, several tongues are formed on one belt end in a sawtoothed or finger shape, and several notches are formed in the other belt end so that it is in a complementary shape with the first end, and then both ends are butted by inserting each tongue into each notch. The flat belt has a thermoplastic resin layer. Thus, both butted ends are heated and bonded by the fusion of the thermoplastic resin so that an endless belt is produced.
International Publication NO. 06/022332 discloses a method for joining the belt ends using a presetter, which has a lower mold portion with an L-shaped cross-section and a movable member provided on the lower mold. The butted portion of the belt is placed on the lower mold and is held by the wall portion of the lower mold and the movable member. While it is held, the butted portion is pressed in the belt thickness direction and is heated. Due to the pressure and heat, the thermoplastic resin of the belt fuses and flows out between both butted belt ends, so that both belt ends are fusion-bonded by the fused resin.
However, when both belt ends are joined by the method above, part of the thermoplastic resin is likely to flow out from the butted portion. The flowing resin forms “flash”, which compromises the flatness of the belt. In addition, the physical properties of the belt joint portion which are formed of the fused resin are different from the rest of the belt. For example, when an oriented polyamide film is used as the belt tension member, the orientation of the film is lost by heat and fusion, which causes the modulus of the joint portion to differ from that of the rest of the belt.
Furthermore, the high pressure in the belt thickness direction has to be applied to the butted portion in the above-mentioned method in order to fill the fused resin between both belt ends. Accordingly, the butted portion is plastically deformed by compression and therefore, the butted portion turns out thinner than the rest of the belt.
Incidentally, the document mentioned above discloses that the belt is held in the belt width direction by the movable member and the wall portion in order to keep the butted portion at a predetermined position. However, it does not disclose that the butted portion is pressed in the belt width direction in order to join both belt ends with the adhesive.